The real key is deciding whether or not you want to own the existing asset long term. 

Been there, done that.....Now you can keep the existing ground level garage and install new structure above to carry the new load.

@Caleb BurkyI'm assuming you are speaking about the subject to or buying a home that is subject to an existing mortgage where the buyer agrees to make payments on the seller's mortgage.

Some other alternatives that may exist in your climate would be furring the exterior shell out, Adding a continuous Rockwool insulation shell, and then creating another layer of exterior siding.

The existing/inherited tenant doesn't sound like he's complaining, so much, as he is letting you know what needs to be done in his unit. 

@Cordell Critchell In @David Krulac's book, he mentions some great tips about developing rural ground, like trying to use the existing roads, instead of paving your own in order to save money while splitting the land.

Blue Spot Home Loans - They said they'd consider, “future rental income” if you secure a lease agreement AND security deposit for rental of your existing condo prior to final loan approval for the condo you will be purchasing. 

Are there existing tenants in place?

We bought this about a year ago and haven't had a chance to do too much yet due to existing leases, but I'd love a strategy moving forward if you (or anyone else) wouldn't mind sharing. 

I would do a cashout refi on your existing property and use that and your existing 50k to invest.